The increasing usage of batteries showing a constant open circuit and/or load potential until the battery is nearly used up as for example, lithium or calcium batteries, especially for military use, has resulted in the increased procurement of these batteries at significant cost. Battery packs may contain a string of 5 to 10 "D-type" cells connected in series along with safety features such as current fuses, thermal fuses and diodes to prevent recharging. One characteristic of a lithium battery is a fairly constant voltage under constant current load until near the very end of discharge, when voltage drops very rapidly. A consequence of this is that it is not possible to measure open circuit voltage or load voltage to determine whether the battery is unused, 25 percent, 50 percent, or 75 percent discharged of its nominal capacity. Thus, when a battery will need replacing is indeterminate. Consequently, when in doubt about the state of a battery, the user will usually throw the old battery away and replace it with a new battery. Many usable batteries are needlessly being thrown away at a significant cost to the user. Fully utilizing batteries for training purposes is most cost effective and desirable. In combat situations, any doubt about the battery rightfully requires its replacement. Development of a method of indicating the state of charge of a battery could allow the complete discharge of batteries used for training and provide confidence in a combat situation since the user will know that the battery is "good" or that replacement is prudent.